In a conventional internal combustion engine of this type, a projecting portion is formed in the center on top face of a piston to form a depression called a cavity in the piston. Thereupon, fuel is injected from a fuel injection valve toward this cavity in the piston at the second half stage of the compression stroke of the internal combustion engine, so that a fuel spray repelled by the cavity is concentrated in the direction of ignition plug (Society of Automotive Engineers of Japan Annual Proceedings 976, Paper No. 9740307, October, 1997).
Thus, the stratification of fuel in the combustion chamber is achieved, and combustion can be produced even with a lean mixture of an air-fuel ratio of about 40. Usually, such a combustion process is referred to as a stratified charge lean burn operation, which serves for reducing fuel consumption at the time of low-load operation of the internal combustion engine.
Also, JP-A-7-119507 has disclosed a combustion system in which at the time of high-load operation, the operation is switched to a so-called homogeneous operation in which fuel is injected during the intake stroke so that the fuel is distributed uniformly in the whole of the combustion chamber.
Further, JP-A-6-81656, JP-A-10-110660, JP-A-7-293259, JP-A-10-30441, JP-A-10-169447, and JP-A-10-896, and U.S. Pat. No. 5,850,816 have disclosed a combustion system in which a tumble air flow is produced in the combustion chamber, and a fuel spray is concentrated around the ignition plug by this tumble air flow.
However, even if any of the above-described combustion systems is used, most of fuel injected from the injection valve sticks to the piston and the wall surface in the combustion chamber, so that there are limitations in increasing fuel efficiency and reducing harmful components (for example, hydrocarbon) in exhaust gas due to the stratified charge operation.
Also, the stratified charge operation cannot be provided under a condition of 80 km/h or 2400 rpm and higher.
A first object of the present invention is to reduce fuel sticking to the piston and the wall surface in the combustion chamber and to decrease HC in exhaust gas.
A second object of the present invention is to increase the output at the time of homogeneous operation.
A third object of the present invention is to provide a fuel injection valve for cylinder injection, in which less fuel sticks to the piston.
A fourth object of the present invention is to enable the stratified charge operation even at a vehicle speed of 80 km/h and higher or at an engine rotational speed of 2400 rpm and higher (for example, in a high speed region where the vehicle speed is 120 km/h or the engine rotational speed is 3200 rpm).